Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Big Ideas: • Characteristics of tectonic plates • How convection in the mantle drives plate motion • 3 types of plate boundaries and typical features at each boundary SCHS-S6C1-PO1, SCHS-S6C1-PO3, SCHS-S6C2-PO4, SCHS-S6C2-PO5 In 1910 Alfred Wegner, a German meteorologist, begins to wonder… • Is there a relationship between all of the continents? • Perhaps all the continents pieces used to be connected? • Continental drift = slow movement over Earth’s surface • Scientists thought Wegner was crazy Two unanswered questions were the main reasons that the hypothesis of continental drift was rejected. • what forces could move continents? • how continents could move without shattering? A. Outer part of Earth consists of thin and rigid pieces called plates, and these plates move slowly and continually. B. 4 main pieces of Evidence: 1. shape of continents = fit together like a puzzle 2. Similarity of fern fossils found on India, Australia and South Africa 3. Similarity of reptile fossils found in South America and Africa 4. Paleomagnetism – where igneous rocks that contain iron record Earth’s magnetic direction at the time the rocks cooled. Fern fossil evidence Paleomagnetism evidence C. Plates: 6 major plates and multiple smaller plates - Each plate ~ 100 km thick - Moving 1 – 20 cm/year. - Average speed is 2 cm/year D. Plate tectonics theory explains the location of mountain ranges, volcanoes, and earthquakes. A tectonic plate is like the hard shell on a boiled egg that has been cracked into pieces or plates. What do you notice? 1. Core – Earth’s internal heat source. 2 sub-layers: a. Inner core: solid iron and nickel b. Outer core: liquid iron c. Heat in the core caused from remnant heat from Earth’s formation & radioactive decay of elements. 2. Mantle – made of plastic-like magma, 2 sub-layers: a. Asthenosphere – lower mantle, made of iron and magnesium. Is semi-solid an can flow like silly putty. b. Lithosphere – upper mantle, rigid and stiff. Does not flow! c. Asthenosphere and Lithosphere separated by a change in density and rock composition. The boundary between is called the Moho discontinuity. 3. Crust – outer skin of the earth. 2 types of crust: a. Oceanic – thinner, denser, basalt rock b. Continental – thicker, less dense, granite rock. B. Earth’s plates are made of either oceanic or continental crust and the lithosphere. These tectonic plates “float” on top of the plastic-like asthenosphere. But how do the plates move? What causes plate motion? A. Answer: convection currents in the mantle B. Convection occurs when a liquid or gas is heated, becomes less dense and rises. When it cools, it gets more dense and sinks, and the process repeats. C. This cycle of heating and cooling drives plate motion. Draw this simple convection current Convection in the asthenosphere • So, now we know why plates move…but what happens at the plate boundaries? Plate Boundary Convergent Divergent Transform Diagram Description 2 plates collide into each other. Mountains or subduction zones form. 2 plates move away from each other. Magma rises to surface. 2 plates slide past each other. A. SUBDUCTION: Oceanic plate (denser) forced under continental (lighter) plate 1. At the subduction zone a deep sea trench is formed where the plate is being forced downwards under the continental plate. 2. Subduction causes rocks to melt, and magma rises to surface to form volcanoes! 3. Examples: Cascades in US, Andes Mountains in South America. B. Mountains can be formed when 2 continental plates collide into each other. 1. Because they both have the same density, neither one subducts under the other. They crumple together. 2. Classic examples are the Himalayas, which are still going up! The Himalayas are still growing today at a rate of 1 - 2 cm a year! Himalayas – 29,029 ft C. When 2 plate move away from each other, magma rises and new crust is formed. 1. This is happening along the mid-Atlantic ridge, which passes through Iceland. 2. If continental crust pulls apart from continental crust then the same process occurs. As magma erupts to the surface to fill the gap, a volcano is created. Mid-Atlantic ridge in Iceland D. When plates move past one another earthquakes occur. 1. Plates are rigid so it is difficult for the plates to slide past each other. 2. The most famous conservative plate margin is the San Andreas Fault on the western coast of North America. San Andreas fault in CA